Successful breeding of Caspian Terns Hydroprogne caspia in the Arctic—part of the new normal?

Abstract

Caspian Terns Hydroprogne caspia have expanded their range in the Eastern Pacific, including southern areas of Alaska, over the past several decades. In 2015, we discovered a pair of Caspian Terns on a small gravel island within Krusenstern Lagoon in Cape Krusenstern National Monument and monitored their breeding status until they successfully fledged two chicks. This site is 653 km north of where Caspian Terns had previously been reported to successfully fledge a chick, and represents the first observations of the species breeding above the Arctic Circle or along the Chukchi Sea coastline. The successful fledging of two chicks at Krusenstern Lagoon suggests that this site, and possibly other Arctic sites, can be suitable breeding habitat. Snow cover and sea-ice duration have decreased dramatically in the Chukchi Sea region over the past four decades; as well, seasonal melt-out has become earlier and freeze-up later. As a result of the longer ice-free season, the Arctic may have recently become available as Caspian Tern breeding habitat as it can now accommodate the long breeding season of this species.